Tridymite-based processing for high purity quartz

Abstract

A process of purifying crystalline quartz to remove impurities within the lattice structure comprising the steps of heating the quartz to the tridymite polymorphic form and evaporatively reacting the heated quartz with an aqueous acid solution reactive with the impurities in the quartz to form water soluble metal salts. The residue of the evaporative reaction is washed with water to dissolve the metal salts leaving purified crystalline quartz. The disclosure also includes the product of the process.

What is claimed is:  
     
       1. A process for removing at least some of the impurities within the lattice structure of crystalline quartz comprising the steps of: 
       A) heating crystalline quartz with impurities within the lattice structure thereof sufficiently to convert a major portion of the crystalline quartz to the tridymite polymorphic form; and,  
       B) depositing the heated crystalline quartz containing the impurities into an aqueous acid solution whereby the acid in the acid solution reacts with at least some of the impurities within the lattice structure of the quartz to form soluble salts and effectively remove the reacted impurities from the lattice structure of the crystalline quartz while simultaneously evaporating the liquid in the aqueous acid solution and thereby cooling the crystalline quartz to a temperature below the tridymite polymorphic form, the volume of the aqueous acid solution selected such that substantially all of the liquid in said aqueous acid solution is evaporated to obtain a residue containing purified quartz crystals and said soluble salts, and the active amount of acid in said aqueous acid solution selected to react with a sufficient amount of the impurities within the lattice structure of the crystalline quartz to thereby reduce the amount of at least some of the impurities in said crystalline quartz.  
     
     
       2. The process of claim  1  wherein step A) comprises heating the crystalline quartz containing the impurities within the lattice structure thereof to a temperature of 870-1470° C. at atmospheric pressure. 
     
     
       3. The process of claim  1  wherein step A) includes heating the crystalline quartz containing the impurities within the lattice structure thereof for a sufficient of time to convert substantially all of the crystalline quartz to the tridymite polymorphic form. 
     
     
       4. The process of claim  1  wherein step B) includes depositing the heated crystalline quartz containing the impurities within the lattice structure thereof in said aqueous acid solution while said aqueous acid solution is at ambient temperature. 
     
     
       5. The process of claim  1  wherein the volume of the aqueous acid solution in step B) is about 0.5 ml of aqueous acid solution per 1.0 g of crystalline quartz containing the impurities within the lattice structure thereof. 
     
     
       6. The process of claim  1  wherein the active amount of acid in said aqueous acid solution in step B) is about ten to ten thousand times the stoichiometric equivalence of the existing impurity content within the lattice structure of the crystalline quartz on a molar basis. 
     
     
       7. The process of claim  1  wherein said aqueous acid solution contains an active acid selected from the group comprising HI, H 2 SO 4 , HBr, HF, and HNO 3 . 
     
     
       8. The process of claim  1  further comprising the step of: 
       C) washing the residue from step B) with water to dissolve the soluble salts and recover the remaining purified quartz crystals.  
     
     
       9. The process of claim  1  further comprising the step of removing any surface impurities from said crystalline quartz prior to step A). 
     
     
       10. The process of claim  1  wherein in step A), said heating the crystalline quartz containing the impurities within the lattice structure thereof is at a temperature of 870-1470° C. for at least one hour. 
     
     
       11. The process of claim  1  wherein in step A), said heating the crystalline quartz containing the impurities within the lattice structure thereof is at a temperature of 870-1470° C. for about 1-4 hours. 
     
     
       12. The process of claim  1  wherein in step B), the volume of said aqueous acid solution is selected such that substantially all of the liquid in said aqueous acid solution is evaporated in a time period of less than ten seconds. 
     
     
       13. The process of claim  1  wherein step B) further includes maintaining said crystalline quartz within the evaporative reactive atmosphere formed as the liquid in the aqueous acid solution is being evaporated until said crystalline quartz is cooled to a stable temperature below the temperature at which said quartz will reocclude impurities into the crystalline lattice structure of the quartz. 
     
     
       14. A process for purifying crystalline quartz containing impurities within the lattice structure thereof to remove at least some of said impurities, the process comprising: 
       a) heating the crystalline quartz to a temperature of 870-1470° C. at atmospheric pressure for about 1-4 hours; and  
       b) depositing the heated crystalline quartz into an aqueous acid solution at ambient temperature with a volume of about 0.5 ml of the aqueous acid solution per 1.0 g of heated crystalline quartz and an active acid content of about ten to ten thousand times the stoichiometric equivalence of the existing impurity content within the lattice structure of the crystalline quartz on a molar basis, wherein the active acid in the aqueous acid solution reacts with at least some of the impurities within the lattice structure of the crystalline quartz to form soluble salts, the liquid in the aqueous acid solution is evaporated thereby cooling the crystalline quartz below the temperature at which said quartz will reocclude impurities into the lattice structure of the crystalline quartz and forming a residue containing a purified crystalline quartz and said soluble salts.  
     
     
       15. The process of claim  14  wherein said aqueous acid solution contains an active acid selected from the group consisting HI, H 2 SO 4 , HBr, HF, and HNO 3 . 
     
     
       16. The process of claim  15  further comprising the step of: 
       c) washing the residue of step b) with water to dissolve the soluble salts and recover the purified crystalline quartz.